grade=float(input("请输入学生的成绩:"))
if 0<=grade<=100:
    if grade>=90:
        print("成绩为:A")
    else:
        if grade>=80:
            print("等级为:B")
        else:
            if grade>=70:
                print("等级为:C")
            else:
                if grade>=60:
                    print("等级为:D")
                else:
                    print("等级为:E")
else:
    print("成绩有误")

